Electron multiplier



April 7, 1964 G. w. GOODRICH ETAL 3,128,408

ELECTRON MULTIPLIER Filed April 20, 1960 3 Sheets-Sheet 1 POWER SUPPLY26 CATHODE 22 .jli III...

ANODE I ANooE CATHODE FIG- 2' ANODE/ exrnoos FIG- 3 INVENTOR.

GEORGE W. GOODRICH WILLIAM C. WILEY ATT NEY April 7, 1964 G. w. GOODRICHETAL 3,128,408

ELECTRON MULTIPLIER Filed April 20, 1960 3 Sheets-Sheet 2 POWERPHOTOCATHODE POWER SUPPLY WAFER OF SECONDARY INVENI'OIZS. GEORGE W.GOODRKH WILLIAM C. WILEY Ap 1964 G. w. GOODRICH ETAL 3,128,408

ELECTRON MULTIPLIER Filed April 20, 1960 5 Sheets-Sheec- 5 POWER SUPPLYFIG. 7

POWER SUPPLY PHOTQCATHODE 8 INVENTOR. GEORGE w. GOODRICH y WILLIAM G.WiLEY Mia/9 ATTORNEY United States Patent 3,128,408 ELEQTRON MULTIPLIERGeorge W. Goodrich, Oak Park, and William C. Wiley,

Northviile, Mich, assignors to The Bendix Corporation, a corporation ofDelaware Filed Apr. 20, 1960, Ser. No. 23,574 21 Claims. (Cl. 313-103)This invention relates to a new type multiplier or light intensifier.This is a continuation in part of our copending application filedSeptember 2, 1958, Serial Number 758, 425, entitled Electron Multiplier,now abandoned. In accordance with the invention, a region defined by asecondary emissive surface is provided with an electric field in adirection to accelerate electrons or other charged particles or photonsthrough the region and to permit the release of secondary electrons whenelectrons strike any part of the emission surface. The multiplier isvery simple and inexpensive to construct.

An object of this invention is to provide a new type electron multiplieror light intensifier.

Other objects and advantages will become apparent from the followingdetailed description and from the appended drawings and claims.

In the drawings:

FIGURE 1 is a perspective view, partly in block form, schematicallyillustrating an electron multiplier constituting one embodiment of thisinvention.

FIGURE 2 is an enlarged sectional view, illustrating the electric fieldproduced in the multiplier shown in FIGURE 1.

FIGURE 3 is an enlarged sectional view illustrating the operation of themultiplier in FIGURE 1.

FIGURE 4 shows how a plurality of multipliers of the type shown inFIGURE 1 may be arranged to intensity a light image.

FIGURES 5 and 6 show another type light intensifier incorporatingapplicants invention.

FIGURES 7 and 8 illustrate different embodiments of applicantsmultiplier.

In FIGURE 1, an electron multiplier generally indicated at 16 issuitably supported in an air evacuated envelope 12. The multiplier 10consists of a straight tube 14 of insulating material, such as glass,coated on its entire inside surface with a conductive coating 16. Theconductive coating 16 is of uniform thickness throughout and is made ofa secondary electron emissive material having a relatively highresistance, such as a tin oxide or carbon compound. The diameter of thetube 14 is relatively small compared to its length.

A source for emitting an incoming signal of electrons, such as a cathode13 is positioned at one end of the multipler 10 to introduce electronsinto the region 20 defined by the coating 16. An anode plate 22 ispositioned at the other end of the multiplier 10 to receive anyelectrons emerging from the region 20. The anode 22 is connected througha resistance 24 to a power supply 26 which applies a constant voltagesuch as +1700 volts to the anode. A constant voltage, such as -1700volts, is applied to the cathode 18 from the power supply 26, so thatthe anode to cathode voltage is 3400 volts.

A constant voltage, such as 1500 volts, is applied to one end of thecoatig 16 adjacent to the cathode 18 and a constant voltage, such as+1500 volts, is applied to the other end of the coating from the powersupply 26 to provide 3000 volts across the multiplier tube 10 andproduce a current flow through the coating. The amount of current flowis relatively small because of the high resistance of the coating 16.This current flow results in a uniform voltage drop per unit distanceacross the surface of the coating 16 and also results in an electricfield 21, substantially parallel to the surface of the coating 16,extending through the region 20 as illustrated in FIGURE 2. As will beappreciated by those skilled in the art, a uniform electric fieldaccompanies a uniform voltage drop. A uniform electric field is a fieldthat has field vectors of the same direction and magnitude throughoutthe field and in the embodiments shown, the field vectors are of thesame magnitude and are all parallel to the surface of emission.

Electrons emitted by the cathode 18, will on the average have an initialvelocity component normal to the axis of the tube 14. Because of thisinitial normal velocity, the electrons entering the region 20 will movetowards the surface of the coating 16 and at the same time the electronswill be accelerated in the direction of the anode 2.2 by the electricfield in the region. After traveling a certain distance in the region20, the electrons will strike the surface of the coating 16. Forexample, some electrons may follow path 28 and other electrons mayfollow path 30 to strike the coating 16 as illustrated in FIGURE 3.

Because of their initial energy and the energy they acquire from theaccelerating electric field, the electrons will strike the coating 16with sufficient energy to produce secondary emission of electrons at aratio greater than 1:1. The secondary electrons thus produced will alsohave a velocity component normal to the surface of the coating 16 andwill, therefore, strike the coating 16 (FIGURE 3) after beingaccelerated a particular distance towards the anode 22, to produce aproportionately increased number of secondary electrons. These electronswill then pass out of the region 20 and impinge upon the anode 22 fordetection of the amplified signal.

Although the electrons have been shown striking the coating 16 onlytwice, it will be understood by persons skilled in the art that thenumber of times that the electrons strike the coating 16 will depend onseveral factors. For example, if the tube 14 were made much longer, theelectrons would strike the coating an increased number of times and,therefore, provide increased multiplication. Reducing the diameter ofthe tube 14 or reducing the electric field to slow up the travel of theelectrons through the region would also increase the number ofcollisions.

As previously mentioned, the electric field produced in the region it)is substantially parallel to the coating 16. The provision of asubstantially parallel field is important in that the field includes asubstantially zero normal component directed into the coating 16 at allpoints so as not to prevent secondary emission from its surface. 7

In addition to having an extremely simple configuration, the multiplierdisclosed above is advantageous in that no critical focusing adjustmentsare required since the lateral spread of the electron beam is limited tothe region 20 defined by the walls of the multiplier, that is thecoating 16. Because the lateral spread of the beam is limited, aplurality of independent multipliers may be arranged in parallelrelationship, as generally indicated at '70 in FIGURE 4, for use as alight intensifier tube. A light image 72 focused on a photo cathode 74would cause the cathode to release electrons which would enter thedifferent tubes in the parallel array 70 and produce secondary emissionto amplify various portions of the image and to produce an intensifiedimage 76 on a fluorescent screen '78. In FIGURE 4, connections from thepower supply are made to the opposite ends of only two tubes.Connections to the opposite ends of the other tubes have not been shownto avoid confusion in the drawing. The intensifier in FIGURE 4 couldalso be operated without a photo cathode by focusing a light imagedirectly at the openings of the tubes. Photons from the light imagewould enter the tubes and anasaoa produce secondary emission ofelectrons to intensify the image. However, the use of a photo cathode ispreferred.

A light intensifier tube may also take the form shown in FIGURES 5 and6. A wafer 100 of secondary emissive material, such as glass having .012inch thickness and having ohm-cm. resistivity, is provided with aplurality of perforations or holes 102 of relatively small size, such as.001 inch in diameter. The holes 102, in substantially parallelrelationship to one another, could be etched through the wafer 100 by aphoto-etching process. A coating 104 of conductive material such assilver is provided on both side surfaces of the wafer 100 leaving theholes uncovered. A photo cathode 106 is positioned adjacent to one sideof the wafer 100 and fluorescent screen 108 is positioned adjacent tothe opposite side of the wafer. A power supply 110 applies constantvoltages to the photo cathode 106, to the conductive coatings on bothsides of the wafer 100 and to the screen 108. For example, constantvoltages such as 4000 volts, -3500 volts, -500 volts and 0 volt may beapplied to the cathode, the conductive coating near the cathode, theopposite conductive coating and to the screen, respectively.

The voltage difference between the conductive coatings on opposite sidesof the wafer 110 will produce a current flow through the wafer and anelectric field through the holes 102 in a direction substantiallyparallel to the axes of the holes. When a light image is focused uponthe cathode, the electrons released by the cathode are introduced intothe holes 102 where they are multiplied in the manner previouslydisclosed to produce an intensified image on the screen 108.

Although the multiplier described above takes the form of the straighttube 10, other configurations can also be used. For example, theembodiment in FIGURE 7 includes a pair of parallel plates 50 and 52disposed close to each other to provide a narrow region between them.The plates 50 and 52 are relatively wide to prevent the loss ofelectrons through the sides of the region. A conductive coating isprovided on the inside surface of each plate and voltages are appliedbetween the ends of the coatings to produce voltage drops across thesurface of the coatings and to produce a substantially parallel electricfield in the region between the plates 50 and 52.

In FIGURE 8 is shown the further embodiment having an outer cylinder 60with open ends and an inner cylinder 62 with closed ends, which areconcentric and have conductive metallic coatings 64 along the peripheryof each cylinder at one end and a similar coating 65 at the other end.Cylinder 60 has a secondary emissive resistive coating 66 on its innersurface which is in contact with coatings 64, 65; cylinder 62 has asecondary emissive resistive coating 68 on its outer surface which is incontact with coatings 64, 65. Adjacent one open end of the concentriccylinders is a photo cathode 70, or other assembly for providingelectrons, ions, photons, or other units which are to be multiplied, andadjacent the other open end of the cylinders is an anode 72. Cathode 70may be annular or of some other configuration as described. A potentialsource 74 supplies a negative potential to cathode 70, such as 1700volts, a slightly more positive potential such as 1500 volts to metallicrings 64 at one end of the cylinders and a much more positive voltagesuch as +1500 volts applied to conductive rings 65 at the other end ofthe cylinder and a slightly more positive potential such as +1700 voltsto the anode or collector 72. In the operation of this embodimentcathode 70 supplies electrons to the electron path which is between theinner cylinder 62 and the outer cylinder 60. Preferably, the end ofcylinder 62 is blocked to prevent electrons from passing through thecenter. The total field at any point is an electric field parallel tothe electron path in this as in the other embodiments. The electrons areaccelerated along this path striking the secondary emissive walls due tothe transverse components in the initial random velocity. In theseembodiments, reproducible multiplication is obtained with the use of avery small and simplified multiplier.

Of course, in order to obtain specific results, certain portions of thewall area which defines the electron path may be open or not coated withthe secondary emissive material. Also, for specific purposes, thecathode assemblies shown schematically herein may include an inputconnected grid or other member for controlling emission therefrom.

Although this invention has been disclosed and illustratcd withreference to particular applications, the principles involved aresusceptible of numerous other applications which will be apparent topersons skilled in the art. The invention is, therefore, to be limitedonly as indicated by the scope of the appended claims.

Having thus described our invention, we claim:

1. A multiplier comprising wall means of secondary electron emissivematerial defining a multiplying path having its longitudinal dimensionsubstantially larger than its lateral dimension,

entrance means into the multiplying path defined by said wall means,

exit means from the multiplying path defined by said wall means spacedfrom said entrance means by said longitudinal dimension,

said multiplying path being totally clear of a field producing wire onthe longitudinal axis of the multiplying path,

said multiplying path being free of any superimposed oscillatingelectric field in a direction transverse to the longitudinal axis,

and means for producing a longitudinal electrical current flow in saidwall means to establish in the multiplying path a total field which isan electric field having a component parallel to the wall means in itslongitudinal direction and having a substantially zero component in atransverse direction to move electrons away from the region of secondaryemission on said wall means so that the primary means for movingelectrons away from the region of secondary emission on said wall meansis the energy of secondary emission.

2. A multiplier as recited in claim 1 wherein said Wall means is a tubedefining the multiplying path.

3. A multiplier as recited in claim 1 wherein said wall means is a pairof parallel plates in closely spaced relation.

4. A multiplier as recited in claim 1 wherein said wall means is a pairof concentric tubes and the multiplying path is defined between theouter surface of the inner tube and the inner surface of the outer tube.

5. A multiplier comprising wall means defining a multiplying path havingits longitudinal dimension substantially larger than its lateraldimension,

said wall means having a secondary electron emissive surface on at leasta portion thereof,

said surface being contiguous with the multiplying path,

entrance means into said multiplying path defined by said wall means atone end of said longitudinal dimension,

exit means from said multiplying path defined by said wall means at theother end of said longitudinal dimension,

said multiplying path being totally clear of a field producing wire onthe longitudinal axis of the multiplying p said multiplying path beingfree of any superimposed oscillating electric field in a directiontransverse to the longitudinal axis,

and means for producing a longitudinal electrical current flow in saidsecondary emissive surface to produce a uniform voltage drop across thesecondary emissive surface in the longitudinal direction and a totalfield in the mulitplying path which is an electric field disposed in adirection such that the primary means for moving electrons away from thesecondary emissive surface is the energy of secondary emission.

6. A multiplier as recited in claim 5 wherein said wall means is a tubedefining the multiplying path.

7. A multiplier comprising wall means defining a multiplying path havingits longitudinal dimension substantially larger than its lateraldimension,

said wall means having a secondary electron emissive surface contiguouswith the multiplying path,

entrance means into the multiplying path defined by said wall means,

exit means from the multiplying path defined by said wall means spacedfrom said entrance means by said longitudinal dimension,

said multiplying path being totally clear of a field producing Wire onthe longitudinal axis of the multiplying p said multiplying path beingfree of any superimposed oscillating electric field in a directiontransverse to the longitudinal axis,

and means for establishing in the multiplying path a total field whichfor a major portion of said path is an electric field substantiallyparallel to the secondary emissive surface in the longitudinaldirection.

8. A multiplier as recited in claim 7 wherein said means forestablishing the field comprising means for producing a longitudinalelectrical current flow in said secondary emissive surface.

9. A multiplier as recited in claim 7 Wherein said wall means is a tubedefining the multiplying path.

10. A multiplier comprising a Wafer of secondary electron emissivematerial having a relatively high resistance,

a plurality of holes extending through the wafer in substantiallyparallel relationship,

the openings of said holes on one side of the wafer being disposed toreceive an incoming signal for multiplication,

the multiplied signal emerging from the holes on the opposite side ofthe wafer,

each of said holes being totally clear of a field producing wire on thelongitudinal axis thereof,

and means for producing an electrical current flow between the oppositesides of the wafer to produce an electric field in each hole in alongitudinal direction substantially parallel to the longitudinal axisof each hole,

said electric field in each hole being the total electric 11. Amultiplier as recited in claim 10 wherein a conductive coating isprovided on each of said opposite sides of the wafer in communicationwith the periphery of said holes,

said means for producing an electrical current flow between the oppositesides of said wafer being connected to said conductive coatings.

12. A multiplier comprising a plurality of straight tubes stacked inparallel relationship,

.:, One end of the stack of tubes being disposed to receive an incomingsignal for multiplication and the multiplied signal emerging from theother end of the stack of tubes,

each of said tubes having an inner surface of secondary electronemissive material,

each of said tubes being totally clear of a field producing wire on thelongitudinal axis thereof,

and means for producing an electrical current flow between the ends ofeach tube to produce throughout substantially all of the region definedby each tube an electric field which is substantially parallel to theinner surface of the tube in the longitudinal direction so that the onlymeans for moving electrons away from the secondary emissive surface isthe energy of secondary emission,

said electric field in each region being the total electric field.

13. A multiplier comprising wall means of secondary electron emissivematerial defining a multiplying path having its longitudinal dimensionsubstantially larger than its lateral dimen- SlOIl,

entrance means into the multiplying path defined by said wall means,

exit means from the multiplying path defined by said wall means spacedfrom said entrance means by said longitudinal dimension,

said multiplying path being totally clear of a field producing Wire onthe longitudinal axis of the multiplying path,

said multiplying path being free of any superimposed oscillatingelectric field in a direction transverse to the longitudinal axis,

means for establishing in the multiplying path a total electric fieldwhich is substantially parallel, in the longitudinal direction, to saidwall means for a major portion of said wall means.

14. A multiplier comprising a straight tube of insulating material,

said tube having its longitudinal dimension substantially greater thanits diameter,

a secondary electron emissive coating of non-insulating materialprovided on the inner surface of the tube of insulating material,

said secondary electron emissive coating of noninsulating materialhaving a relatively high predetermined resistance to provide a path foran electrical current flow,

said tube being totally clear of a field producing Wire on thelongitudinal axis of the region defined by the coating,

and means for producing an electrical current flow in the secondaryelectron emissive coating between the ends of the tube therebyestablishing a total electric field in the region defined by the coatingwhich is substantially parallel to the coating in the longitudinaldirection.

15. A multiplier comprising a tube having its longitudinal dimensionsubstantially greater than its diameter,

said tube having a secondary electron emissive inner surface,

said tube being totally clear of a field producing wire on thelongitudinal axis of the region defined by the tube,

and means for producing a uniform voltage drop across the secondaryemissive inner surface of the tube in the longitudinal direction toproduce in the region defined by the tube a total electric field whichis disposed in a direction such that the primary means for movingelectrons away from the secondary emissive surface is the energy ofsecondary emission.

16. A multiplier as recited in claim 15 wherein the electric field issubstantially parallel to the inner surface of the tube in thelongitudinal direction.

17. A multiplier comprising wall means defining a multiplying pathhaving its longitudinal dimension substantially larger than its lateraldimension,

said wall means having a secondary electron emissive surface contiguouswith the multiplying path,

means for introducing a signal to be multiplied into the multiplyingpath,

means for receiving the multiplied signal emerging from the multiplyingpath,

said multiplying path being totally clear of a field producing wire onthe longitudinal axis of the multiplying path,

said multiplying path being free of any superimposed oscillatingelectric field in a direction transverse to the longitudinal axis,

an air evacu ed envelope enclosing said wall means, said lyfiiicingmeans and said receiving means,

and me for producing a longitudinal electrical current flow in saidsecondary emissive surface to produce a uniform voltage drop across thesecondary emissive surface in the longitudinal direction and a totalfield in the multiplying path which is an electric field disposed in adirection such that the primary means for moving electrons away from thesecondary emissive surface is the energy of secondary emission.

18. A multiplier comprising a plurality of tubes stacked in parallelrelationship,

means for introducing into one end of the stack of tubes a signal to bemultiplied,

the multiplied signal emerging from the other end of the stack of tubes,

each of said tubes having an inner surface of secondary electronemissive material and defining a region totally clear of a fieldproducing wire on the longitudinal axis of the region,

and means for producing an electrical current flow between the ends ofeach tube to produce throughout substantially all of the region definedby each tube an electric field which is substantially parallel in thelongitudinal direction to the inner surface of the tube,

said electric field in each region being the total electric field.

19. A multiplier comprising a plurality of tubes stacked in parallelrelationship,

means for introducing into one end of the stack of tubes a signal to bemultiplied,

the multiplied signal emerging from the other end of the stack of tubes,

means for receiving the multiplied signal emerging from the stack oftubes,

each of said tubes having an inner surface of secondary electronemissive material and defining a region totally clear of a fieldproducing wire on the longitudinal axis of the region,

an air evacuated envelope enclosing said stack of tubes, saidintroducing means and said receiving means,

and means for producing an electrical current flow between the ends ofeach tube to produce a uniform voltage drop across the inner surface ofthe tube in the longitudinal direction and an electric field in theregion defined by the tube,

the electric field in each region being the total field.

20. A multiplier comprising,

a tube of insulating material,

said tube having its longitudinal dimension substantially greater thanits diameter,

a secondary electron emissive coating of noninsulating material providedon the inner surface of the tube,

said coating being contiguous with the multiplying path having arelatively high resistance,

one end of the tube being disposed to receive an incoming signal formultiplication and the multiplied signal emerging from the other end ofthe tube,

means for receiving the multiplied signal emerging from the tube,

said tube being totally clear of a field producing wire on thelongitudinal axis of the region defined by the coating,

and means for producing an electrical current flow in the coatingbetween the ends of the tube to produce a uniform voltage drop acrossthe coating in the longitudinal direction and to establish an electricfield in the region defined by the tube,

said electric field being the total field in said region.

21. A multiplier comprising wall means of secondary electron emissivematerial defining a multiplying path having its longitudinal dimensionsubstantially larger than its lateral dimen- SlOIl,

entrance means into the multiplying path defined by said wall means,

exit means from the multiplying path defined by said wall means spacedfrom said entrance means by said longitudinal dimension,

said multiplying path being totally clear of a field producing wire onthe longitudinal axis of the multiplying path,

said multiplying path being free of any superimposed oscillatingelectric field in a direction transverse to the longitudinal axis,

means for producing a longitudinal current fiow in said wall means toproduce along said wall means an electric potential which provides theentire field in said multiplying path.

References (Jilted in the file of this patent UNITED STATES PATENTS2,203,048 Farnsworth June 4, 1940 2,210,034 Keyston Aug. 6, 19403,062,962 McGee Nov. 6, 1962 FOREIGN PATENTS 884,059 Germany July 23,1953 916,257 France Aug. 12, 1946 OTHER REFERENCES Terman: RadioEngineers Handbook, published by McGraw-Hill (New York), 1943.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,128,408 April 7, 1964 George W. Goodrich et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected belo' Column 1, line l8, for "emission" read emissive line 63,for "coatig" read coating column 3, line 7, for "10 ohm-cm." read l0 1ohm-cm.

Signed and sealed this 13th day of October 1964.

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A MULTIPLIER COMPRISING WALL MEANS OF SECONDARY ELECTRON EMISSIVE MATERIAL DEFINING A MULTIPLYING PATH HAVING ITS LONGITUDINAL DIMENSION SUBSTANTIALLY LARGER THAN ITS LATERAL DIMENSION, ENTRANCE MEANS INTO THE MULTIPLYING PATH DEFINED BY SAID WALL MEANS, EXIT MEANS FROM THE MULTIPLYING PATH DEFINED BY SAID WALL MEANS SPACED FROM SAID ENTRANCE MEANS BY SAID LONGITUDINAL DIMENSION, SAID MULTIPLYING PATH BEING TOTALLY CLEAR OF A FIELD PRODUCING WIRE ON THE LONGITUDINAL AXIS OF THE MULTIPLYING PATH, SAID MULTIPLYING PATH BEING FREE OF ANY SUPERIMPOSED OSCILLATING ELECTRIC FIELD IN A DIRECTION TRANSVERSE TO THE LONGITUDINAL AXIS, 